In processing photographic films, especially X-ray films, it is highly advantageous to complete the processing in a very short period of time. To accomplish this objective, it is common practice to process such films using a roller transport processor and to carry out the processing without an intervening washing step between the steps of developing and fixing. This method of processing is described, for example, in U.S. Pat. No. 3,545,971. To facilitate the use of a roller transport processor, both the developer and the fixer typically contain a hardening agent, with the hardening agent usually being an aldehyde in the developer and an aluminum salt in the fixer. Boric acid is often incorporated in the fixer used in the aforesaid process to prevent the formation of sludge resulting from precipitation of aluminum hydroxide when the fixer is contaminated by developer carry-in. Such use of boric acid is described, for example, in U.S. Pat. No. 4,046,570. The hardening fixer composition described in this patent also contains a 1-hydroxy-alkylidene diphosphonic acid, in which the alkylidene group contains from 2 to 5 carbon atoms to retard formation of aluminum hydroxide. The 1-hydroxy-alkylidene diphosphonic acid partially or completely replace boric acid in the hardening fixer composition.
Another method to reduce the precipitation of aluminum hydroxide has been described in Research Disclosure 17549, wherein a combination of a diphosphonic acid, such as a hydroxyalkylidene diphosphonic acid, and an aminopolycarboxylic acid, such as a 1,3-diamino-2-propanol tetraacetic acid, has the tendency for aluminum hydroxyde precipitates, as a result of carrying of aluminum salt hardening agent contacting in the hardening baths. The diphosphonic acid and the aminopolycarboxylic acid are effective in the stabilizing bath in small concentrations such as amounts of each of about one gram per liter or less. The pH of said color stabilizing bath is in the range from about 6 to about 11.
Japanese Patent Application 05-323,525 describes a black-and-white fixer solution comprising aminopolycarboxylic acids and/or phosphonic acids as chelating agent, preventing the water fur and odour. The fixer composition is substantially free of ammonium ions and substantially free of aluminum hardener, the amount of the hardener being lower than 0.01 mol/l that is the minimum amount known in the art to give the fixer composition a hardening activity, as described in Research Disclosure 16768 and in U.S. Pat. No. 4,046,570.
To further promote the objective of a very short total processing time, it is advantageous to employ ammonium thiosulfate as the fixing agent, because it acts more rapidly than alternative fixing agents such as sodium thiosulfate, as described in GB 1,290,026. Thus, a particularly desirable fixer is one which contains ammonium thiosulfate and is free of boric acid; however, it has been found that a very serious problem of crystal formation occurs. In particular, crystals are deposited from the fixer on the walls of the fixer tank and on the roller assemblies. In addition, the crystalline deposit displays a tendency to absorb additional fixer, thereby resulting in movement of "creep" along processor parts and tank walls. Research Disclosure 18728 discloses a number of agents incorporated in the hardening fixer and which suppress crystal formation. Useful agents are, for example, aminopolyphosphonic acids, such as diethylenetriaminepentamethylenephosphonic acid, and aminopolycarboxylic acids, such as 1,3-diamino-2-propanol tetraacetic acid.
EP 486,909 describes ammonium-free fixing bath containing a complex building agent, e.g., nitrilodiacetic monopropionic acid, useful for silver halide photographic materials. The baths exhibit good fixing speed and no deposition.
The pH of these fixer baths is normally around 4.00-4.30, because at higher pH, expecially more than 5.00, there is precipitation of Al(OH).sub.3. On the other hand, lower pH is correlated with high SO.sub.2 evolution, which is environmentally dangerous. It could be useful to have a photographic fixer composition showing a reduced tendency to form an aluminum hydroxyde precipitation at pH values higher than those of standard fixer compositions. In fact, a fixer composition working at said high pH value could be also advantageous from an environmental point of view, showing a reduced SO.sub.2 emission.